Liquid crystal displays are applicable to small-sized information terminal devices and projection devices and are in demand in a wide range of fields as the personal computer market expands along with the rapid progress of information processing technology. The future development of liquid crystal displays has been drawing much attention.
Particularly, for liquid crystal displays for personal computers and televisions, the demand for making the display screens larger, with higher definition, as well as lighter, is increasing. Development has also been made to have larger and thinner glass substrates in order to meet such increasing demand. As glass substrates get larger in size and thinner, a high-level substrate dividing technique is in demand for dividing glass substrates into desired sizes with high accuracy.
Brittle substrates such as glass substrates may be divided into sections by performing a scribe step of forming a linear scribe line extending in a desired dividing direction on the surface of a glass substrate and a break step of dividing the glass substrate along the scribe lines by applying a bending moment along the scribe line formed on the surface of the glass substrate.
In the scribe step of forming the scribe line on the glass substrate, if the scribe line which is a line with a vertical crack can be formed deep into the glass substrate and vertical to the surface of the glass substrate, it is possible to improve the accuracy level when the substrate is divided into sections along the scribe line in the break step to be performed later; therefore, it is important to make the vertical crack deep.
For example, using a manually-operated cutter as disclosed in the Japanese Unexamined Utility Model Application Publication No. 59-88429, a scribe line may be formed on the surface of a brittle material substrate by rolling a wheel tip attached at the tip of a cutter over the surface of the glass substrate with pressure. Further, it is also possible to use an apparatus disclosed in the Japanese Unexamined Patent Application Publication No. 55-116635 for forming a number of scribe lines on the surfaces of a plurality of brittle material substrates continuously and automatically.
A method of forming a scribe line by cutting the surface of a glass substrate with a point diamond is not suitable for forming a scribe line on a glass substrate used in a liquid crystal display device because cullet (glass shavings) is generated without exception in the process of cutting the glass substrate with the point diamond.
Further, according to the method wherein a wheel tip being rotatable held is rolled over the surface of a glass substrate with pressure, a vertical crack is generated by pressing the wheel tip against the surface of the substrate using a lifting and lowering mechanism such as an air cylinder.
With such a pressing method using a lifting and lowering mechanism, however, it is not possible to easily form a vertical crack that has a sufficient depth in the surface of the glass substrate unless the pressure applied by the lifting and lowering mechanism is large. On the other hand, in case the pressure being applied is large, when the wheel tip is made to proceed up onto an edge of a glass substrate, there is a possibility that the edge of the glass substrate may be damaged, for example, it may be chipped off. Besides, in case the pressure being applied is large, there are possibilities of other problems; for example, a crack (a horizontal crack) may be generated in an unwanted direction in the plane portion of a glass substrate, and such a crack may cause chipping in a division plans or in an edge portion of the glass substrate including a division plane, when the glass substrate is divided into sections. In addition, also with this method, glass cullet is generated in the scribing process.
Further, in the case where a glass substrate has a “warp”, another problem Is that the wheel tip is not able to follow unevenness resulting from the “warp” at the surface of the substrate, and therefore it is impossible to obtain an appropriate vertical crack in the surface of the glass substrate.
In order to solve the aforementioned problems, the present invention aims to provide a scribe line forming apparatus and a scribe line forming method by which it is possible to generate a vertical crack having a sufficient depth in a glass substrate, without causing a problem such as an edge of the glass substrate being chipped off.